Many types of fuel filters (also known as "separators") are known in the prior art. A popular type of filter construction is a type that has a filter head to which a replaceable "spin-on" element is attached. The head is a permanent part of the fuel system of the vehicle and includes inlet and outlet connections to the fuel lines. The filter element may be readily removed from the filter head and a new one attached without removing the filter head from the fuel line connections.
One problem associated with filters, and particularly filters for diesel fuel, is that during cold starting conditions, the fuel can have a low viscosity--making it difficult for the fuel to pass through the filter. The cold fuel can also wax or plug the filter media. This is a well-known issue, and many devices have been developed in an attempt to solve this. For example, one fuel filter includes a heater provided internally of the filter housing to heat the fuel and the media as the fuel passes through the filter (see, e.g., Stone, U.S. Pat. No. 5,547,572). While such heaters help solve the problem of waxing or plugging, it is believed that many such heaters have been relatively complex assemblies with a number of components that are sometimes difficult to assemble. It is therefore believed there is a need for heaters that are simple to manufacture and assemble, and yet which are still efficient, reliable, and long-lasting.
Another problem is that elements with different efficiencies, applications, and/or qualities can sometimes fit on the same filter head. Periodic replacement of the element is necessary such that the filter element will not become so loaded with impurities that fuel flow is restricted. Replacing the element also ensures that impurities are removed from the fuel before it is delivered to downstream components such as fuel injection pumps and fuel injectors, where such contaminants may cause damage. It is important to replace a spent element with the same type of element. It is also important to run the filter with an element installed. Using the wrong type of element or failing to use any element can allow damage to occur to the downstream components. Certain elements have been designed whereby the element can only fit a certain filter head, and where the filter will not operate without such a filter element installed (see, e.g., Clausen, U.S. Pat. No. 5,643,446). While this has provided some protection, it is believed that there is still a need for simple, compact, easy to assemble elements that can only be used with a specific filter head, and where the filter will not operate without a filter element installed.
A still further problem arises when a fresh element is installed on the filter head. When the spent element is removed, the element is filled with fuel. The fresh element, when it is installed, is not. Therefore, the new element introduces an air pocket into the system. The air pocket may prevent fuel flow if fuel is drawn through the head and element by vacuum produced by a downstream fuel pump. A large slug of air in the system may also cause damage to downstream components such as an injector pump or fuel injectors.
It is known to install a priming pump on the filter head to eliminate the air pocket. The pump is actuated by alternatingly depressing and releasing a pump cap on the filter head. One type of priming pump is located in the fluid flow path between the inlet to the head and the in-flow area of the filter element, with a pair of spherical valve elements controlling the flow of fuel through the head (see, e.g., Jensen, U.S. Pat. No. 5,362,392). This type of pump is reliable, but has flow passages that require careful manufacturing so that the passages are maintained within close tolerances. The passages are also somewhat complicated to manufacture, which adds to the overall cost of the pump. It is therefor believed there is also a need for a filter head with a manual priming pump that is simple to manufacture and assemble, and yet is still reliable.
As such, it is believed there exists a need for an improved filter head, and filter element therefor, that overcomes the drawbacks identified above.